Systems and methods for measuring gas flux

ABSTRACT

Systems and methods for measuring gas flux are disclosed. One method for calculating gas flux includes: receiving a master clock signal from a global positioning system (GPS) module; transmitting a clock synchronization signal that is based on the master clock signal to a measurement subsystem configured to measure environmental data, wherein the measurement subsystem comprises at least two clocks; receiving the environmental data from the measurement subsystem, wherein the environmental data is associated with the at least two clocks; and calculating gas flux based on the environmental data received from the measurement subsystem.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation application of U.S. Non-provisionalapplication Ser. No. 14/039,686, filed Sep. 27, 2013, the contents ofwhich are each hereby incorporated by reference.

BACKGROUND

The present disclosure relates generally to gas analysis and, moreparticularly, to systems and methods for measuring gas flux.

The increasing concentrations of carbon dioxide and other traces gases(e.g., H₂O, CH₄, N₂O, NH₃, etc.) in the atmosphere, and the resultinggreenhouse effect and climate change, have become important topics forscientific research. In order to understand the global carbon balance,it is necessary to determine the rate at which carbon dioxide and energyexchanges between the atmosphere and terrestrial and oceanic ecosystems.The air within a few hundred meters above the earth's surface is mostlyturbulent, so that turbulent structures (e.g., vortices of variablesizes) called “eddies” are responsible for the vertical transport ofmost of the gases, including carbon dioxide and water vapor, and alsoheat and momentum between the surface and the atmosphere. The rates ofsuch transport can be calculated from simultaneous, high-frequencymeasurements of the vertical component of wind speed, the concentrationsof carbon dioxide and water vapor, and the air temperature. Similarcalculations can be made to measure methane or other gases of interest,for example.

One issue involved in computing turbulent gas flux rates is thatmultiple measurement devices are used to provide the necessary data,including gas analyzers, temperature sensors, wind speed measuringdevices, and/or water vapor analyzers, among others. Each of thesemeasurement devices operates on its own clock. In order to properlycompute turbulent gas flux rates, the clocks of the differentmeasurement devices used for accumulating data should be synchronized.

In one conventional approach, analog measurement data is transmitted toa data logger that logs the data and then samples the analog data.However, not all measurement devices provide analog outputs.

Another conventional approach provides for a synchronous bus between themeasurement devices that synchronizes the clocks of the multiplemeasurement devices. The main problem with synchronous buses is thatthey do not scale well. Also, synchronous buses tend to be proprietaryto each manufacturer.

Also, in many conventional approaches, the measurement devices and anyother devices at the sampling site do not offer any processing oranalysis of the raw data. Data is collected over a period of time, forexample over two weeks, and is stored at the sampling site, typically ina storage device coupled to or included in one of the measurementdevices. A scientist must then go out to the sampling site to retrievethe data on the storage device for analysis. This conventional approachis very cumbersome since going to the sampling site on a repeated basisis tedious and time consuming, and can be dangerous if the sampling isbeing performed in remote or difficult-to-access locations.

Accordingly, it is desirable to provide systems and methods thatovercome the above and other limitations of conventional approaches tomeasuring gas flux.

SUMMARY

One embodiment provides a system for measuring gas flux. The systemincludes a measurement subsystem configured to measure environmentaldata associated with measuring the gas flux, wherein the measurementsubsystem comprises at least two clocks, and a processing unit in signalcommunication with the measurement subsystem. The processing unit isconfigured to: transmit a signal over a packet-switched network to themeasurement subsystem so as to synchronize the at least two clocks inthe measurement subsystem, receive the environmental data from themeasurement subsystem, wherein the environmental data is associated withthe at least two clocks, and calculate the gas flux based on theenvironmental data received from the measurement subsystem.

Another embodiment provides a computing device for calculating gas flux.The computing device includes: a first interface configured to receive amaster clock signal from a global positioning system (GPS) module; asecond interface configured to transmit a clock synchronization signalthat is based on the master clock signal to a measurement subsystemconfigured to measure environmental data, wherein the measurementsubsystem comprises at least two clocks; a third interface configured toreceive the environmental data from the measurement subsystem, whereinthe environmental data is associated with the at least two clocks; and aprocessing unit configured to calculate gas flux based on theenvironmental data received from the measurement subsystem.

Yet another embodiment provides a method for calculating gas flux. Themethod includes: receiving a master clock signal from a globalpositioning system (GPS) module; transmitting a clock synchronizationsignal that is based on the master clock signal to a measurementsubsystem configured to measure environmental data, wherein themeasurement subsystem comprises at least two clocks; receiving theenvironmental data from the measurement subsystem, wherein theenvironmental data is associated with the at least two clocks; andcalculating gas flux based on the environmental data received from themeasurement subsystem.

Reference to the remaining portions of the specification, including thedrawings and claims, will realize other features and advantages of thepresent disclosure. Further features and advantages of the presentdisclosure, as well as the structure and operation of variousembodiments of the present disclosure, are described in detail belowwith respect to the accompanying drawings. In the drawings, likereference numbers indicate identical or functionally similar elements.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a gas flux measurement system, according to oneembodiment.

FIG. 2 illustrates a process of measuring gas flux, according to oneembodiment.

FIG. 3 is a block diagram of example functional components for acomputing subsystem, according to one embodiment.

FIG. 4 is a flow diagram of method steps for measuring gas flux,according to one embodiment.

FIG. 5 is a conceptual diagram of a computing subsystem, according toone embodiment.

DETAILED DESCRIPTION

Embodiments of the disclosure provide systems and methods for measuringgas flux based on synchronizing hardware clocks included in two or moremeasurement instruments. Each measurement instrument includes a softwareclock and a hardware clock. A computing subsystem is communicativelycoupled to the measurement instruments and also to a GPS (globalpositioning system) module. The GPS module is configured to send pulsesto the computing subsystem with GPS data that includes time data. Acontroller included in the computing subsystem is configured to receivethe pulses from the GPS module and to set a master clock included in thecomputing subsystem.

The computing subsystem is configured to synchronize the software clocksof the measurement instruments to the master clock via a packet-switchednetwork. Each measurement instrument further includes a controller thatis configured to synchronize the hardware clock included in themeasurement instrument to the synchronized software clock included inthe measurement instrument. Raw data that is output by the measurementinstruments, which is now synchronized in time, is then transmitted tothe computing subsystem for computation or further processing. Gas fluxmeasurements are computed based on the raw data. The computed gas fluxmeasurements are then transmitted to one or more of the measurementinstruments and/or to a monitoring software device for storage,analysis, and consumption.

Advantageously, embodiments of the disclosure provide for real-time ornear real-time gas flux measurements. Also, the disclosed systemsynchronizes the clocks over an asynchronous network (such as, forexample, Ethernet), which provides for ease of installation andmaintenance.

FIG. 1 illustrates a gas flux measurement system, according to oneembodiment. As shown, the system includes gas analyzer 102, gas analyzer106, wind speed measuring device 104, computing subsystem 110, and webmonitor device 116, which are interconnected via a data communicationpath 126. The system also includes a GPS (global positioning system)module 112 communicatively coupled to the computing subsystem 110.

The data communication path 126 can be physical wires/cabling, or a formof wireless communication link (e.g., radio, WiFi, cellular dataconnection, satellite data connection, etc.), or some combination ofboth. In one embodiment, the data communication path 126 comprises anEthernet connection.

The gas analyzer 102 can be any analyzer suitable for measuring thedensity of a target gas, i.e., the gas of interest that is to beanalyzed. For example, methane (CH₄) is a commonly measured gas. Methaneanalyzers for measuring methane density are commercially available, suchas the LI-7700 Open Path CH₄ Analyzer, which is designed, manufactured,and sold by the assignee of the present application. Generally,absorption-based gas analyzers use absorption of light from either (i) abroadband non-dispersive infrared (NDIR) source equipped with suitableoptical filter, or (ii) a narrowband laser source to measure the densityof the target gas of interest. The light is selectively absorbed by thegas as it crosses the light path between the light source and a detectorin a region called the sampling volume (also variously referred to as“sample volume,” “sampling path,” and so on). The gas analyzer 102outputs raw gas density measurement data via the data communication path126 based on the measured absorption characteristics.

Two categories of gas analyzers are conventionally known and are definedby the nature of the sampling volume. An “open path” type gas analyzeris one in which the sampling volume and the optical path are exposed tothe environment containing the gas to be analyzed. A “closed path” gasanalyzer is one in which the sampling volume is enclosed in a tube (inwhich case the sampling volume can be referred to as the sample cell)and the optical path lies within the tube, and the gas to be measured ispassed within the tube. In accordance with the present application, thegas analyzer 102 can be either an open path analyzer or a closed pathanalyzer or a combination of the two.

Gas analyzer 106 can also be any analyzer suitable for measuring thedensity of a target gas. In one embodiment, gas analyzer 106 isconfigured to measure carbon dioxide (CO₂) gas and water vapor (H₂O).One example of such a gas analyzer is the LI-7550 Analyzer, which isdesigned, manufactured, and sold by the assignee of the presentapplication. For example, the gas analyzer 106 may be a high-speed,high-precision, non-dispersive infrared gas analyzer that accuratelymeasures densities of carbon dioxide and water vapor in situ. Forexample, a chopper wheel carrying a plurality of spectral filterssequentially passes radiation from a source at discrete wave-lengthsthrough each cell in sequence. The amount of radiation absorbed by thegas is detected to determine the concentrations of certain components inthe gas. The gas analyzer 106 outputs raw gas density measurement datavia the data communication path 126 based on the measured absorptioncharacteristics.

The wind speed measuring device 104 produces a measure of the speed ofthe moving air in the vicinity of the gas analyzer 102 and/or gasanalyzer 106 and outputs corresponding wind speed measurement data viathe data communication path 126. In some embodiments, the wind speedmeasurement in accordance with the present disclosure may be verticalwind speed. An instrument commonly used to measure wind speed is knownas an anemometer. This instrument is commonly used with open path gasanalyzers, for example. There are several types of anemometers, rangingin complexity. The most basic models of anemometers measure the windspeed, while the more complex models can measure wind speed, winddirection, and/or atmospheric pressure. One particularly useful type ofanemometer is a sonic anemometer that typically provides high-speed(e.g., more than 10 Hz) measurements. It will be appreciated of coursethat other wind speed measurement devices and techniques can be used.

In the embodiment shown in FIG. 1, the raw data output from the gasanalyzer 102 via data communication path 126 is transmitted to the gasanalyzer 106. The raw data output from the wind speed measuring device104 via data communication path 126 is also transmitted to the gasanalyzer 106. The raw data output by the gas analyzer 106, as well asthe raw data received by the gas analyzer 106 from the gas analyzer 102and the wind speed measuring device 104, are then transmitted via thedata communication path 126 to the computing subsystem 110. In oneimplementation, when the data communication path 126 is an Ethernetconnection, an Ethernet switch 130 included in the gas analyzer 106 isconfigured to receive the raw data from the gas analyzer 102 and thewind speed measuring device 104 and forward the raw data to thecomputing subsystem 110. As shown, each of the gas analyzer 102 and thewind speed measuring device 104 is connected in series with the gasanalyzer 106, which is configured to receive and forward the raw datafrom the gas analyzer 102 and the wind speed measuring device 104,respectively.

In some embodiments, a storage device (not shown) may be coupled to thegas analyzer 106. For example, the storage device may comprise a USB(Universal Serial Bus) storage device that includes non-volatile memory.The raw measurement data measured by the gas analyzers 102, 106 and bythe wind speed measuring device 104 can be stored in the storage deviceof the gas analyzer 106.

In another embodiment, each of the gas analyzer 102, the wind speedmeasuring device 104, and the gas analyzer 106 is directly connected tothe computing subsystem 110 via the data communication path 126.

Also, in some embodiments, a single gas analyzer is configured tomeasure methane, carbon dioxide, and water vapor. Such a gas analyzercould be coupled to the computing subsystem 110 via data communicationspath 126.

In other embodiments, a water vapor analyzer may be used as a separategas analyzer from a gas analyzer that measures carbon dioxide gas. Suchwater vapor gas analyzer might include a hygrometer or other analyzerand could be coupled to the computing subsystem 110 via datacommunications path 126. In certain environments, the water content canbe significant enough to considerably affect the absorption lineshape ofthe target gas and the resulting density measurement. Dilution by watervapor causes an actual physical change in partial pressure and a changein actual density when compared to dry. In addition, water vapor affectsabsorption by line broadening, which consequently affects the resultingdensity measurement. Under such conditions, more accurate results areachieved if the water content is measured and factored into thecomputations. In some embodiments, atmospheric pressure is also measuredand is used to obtain a correct gas concentration measurement. U.S. Pat.No. 8,433,525, which is hereby incorporated by reference in itsentirety, provides a more detailed discussion regarding such water vaporeffects on measurements. However, if the environment where the targetgas is being analyzed is sufficiently dry, the water content may nothave any significant affect on density measurements of the target gas.In that case, the cost and complexity of coordinating gas densitymeasurements with water vapor measurements can be dispensed with and thewater vapor analyzer would not be required.

In some embodiments, a temperature sensor (not shown) may be used tomeasure ambient temperature in the proximity of the gas densitymeasurements. Typical devices for the temperature sensor include afine-wire thermocouple, a sonic anemometer, and in general any devicethat can provide fast gas temperature measurements. In accordance withthe present disclosure, the temperature sensor can be positioned inproximity to the sampling volume of the gas analyzers 102 and/or 106, oralternatively within the sampling volume of the gas analyzers 102 and/or106. Any other type of measurement device can also be used and is withinthe scope of embodiments of the disclosure.

As shown in FIG. 1, the gas analyzer 102, the wind speed measuringdevice 104, and the gas analyzer 106 communicate data to the computingsubsystem 110 via the data communication path 126. The computingsubsystem 110 includes a suitable data processing component (e.g., oneor more processors), data storage devices, and communication interfaces.The computing subsystem 110 may include many more components than thoseshown in FIG. 1. However, it is not necessary that all of thesegenerally conventional components be shown in order to discloseillustrative embodiments for practicing the present disclosure.

Typical devices that can serve as the data storage device includetraditional disk storage devices such as hard disk drives, floppy diskdrives, writable CD-ROMs, other removable storage formats, and the like.Data storage can also include flash memory devices such as flash drives,or other similar static storage devices. Data storage is typically ahigh capacity storage device for storing the large amounts ofmeasurement data that can be received by the computing subsystem 110during a data collection session. The data storage may be called upon tostore data from several data collection sessions.

The computing subsystem 110 can be configured to any level ofsophistication as needed for a particular implementation of themeasurement devices shown in the system of FIG. 1, and can be built tosurvive rugged field deployments for months or even years on end.

In accordance with some embodiments, the computing subsystem 110 can bea full-featured and sophisticated data logging component that is notonly able to communicate with the measurement devices via the datacommunication path 126 and receive measurement data from the measurementdevices to be stored in the data storage, but also includes computerprogram code, such as computation software 113, to calculate gas fluxvalues of the target gas of interest. The target gas of interest can becarbon dioxide, water vapor, methane, or any other gas. In oneembodiment, the computing subsystem 110 is located at the samemeasurement site as the measurement devices (i.e., the same measurementsite as the gas analyzers 102 and/or 106, and the wind speed measuringdevice 104).

According to various embodiments, the Eddy Covariance (EC) method is themost direct and reliable method for gas flux measurement calculationsavailable to date. EC is a dominating method used in most turbulent fluxmeasurements. EC is used as a standard for other turbulent fluxmeasurement methods, and for any atmospheric flux measurement methods.However, EC requires high-speed gas concentration measurements (e.g.,5-10 Hz (Hertz) or more) in addition to the high-speed vertical windspeed measurements (e.g., 5-10 Hz or more). The computation software 113is configured to receive the gas concentration measurements and thevertical wind speed measurements and calculate the gas flux valuestherefrom. The calculated gas flux values may be computed as a gas fluxbased on measurement taken over a certain time period, for example, 30minutes. The calculated gas flux values can then be transmitted via thedata communication path 126 to the gas analyzer 106 for storage in astorage device and/or may be transmitted via the data communication path126, or another data communication path (not shown) to the web monitordevice 116. In some embodiments, the web monitor device 116 is locatedat a remote location from the measurement site. Because the calculatedgas flux values are relatively small in data size compared to thehigh-speed gas concentration measurements and vertical wind speedmeasurements, the data connection by which the calculated gas fluxvalues are transmitted to one or more measurement devices and/or aremote computing device can be a small-bandwidth connection. Examples ofdata connections that could be used include Ethernet, cellular network,or satellite network, among others.

In some embodiments, the data communication path between the computingsubsystem 110 and the measurement devices (i.e., the gas analyzers 102and/or 106 and the wind speed measuring device 104) is different fromthe data communication path between the computing subsystem 110 and theweb monitor device 116. In some embodiments, the data communicationpaths are the same.

As also shown in FIG. 1, computing subsystem 110 includes a master clock115 and controller 114. The controller 114, which may be implemented asa proportional-integral (PI) control system, is configured to receivedata pulses from the GPS module 112. The pulses may be PPS(pulse-per-second) pulses. The controller 114 is configured to set themaster clock 115 included in the computing subsystem 110 according tothe data pulses from the GPS module 112. The master clock 115 can be asoftware clock or a hardware clock.

As also shown, gas analyzer 102, wind speed measuring device 104, andgas analyzer 106 include slave clocks 120A, 102B, and 120C,respectively. In some embodiments, the slave clocks 120A-120C comprisesoftware clocks.

Gas analyzer 102, wind speed measuring device 104, and gas analyzer 106further include controllers 122A, 122B, and 122C, respectively. In someembodiments, controllers 122A-122C may be similar to the controller 114included in the computing subsystem 110.

Gas analyzer 102, wind speed measuring device 104, and gas analyzer 106further include hardware clocks 124A, 124B, and 124C, respectively. Inone embodiment, the hardware clocks 124A-124C are implemented as FPGAs(field-programmable gate arrays).

In order for the computing subsystem 110 to accurately compute gas fluxvalues, the measurement data measured by the various measurement devicesshould be synchronized in time. As such, the hardware clocks 124A-124Cshould be synchronized.

The IEEE 1588 protocol, “Standard for a Precision Clock SynchronizationProtocol for Networked Measurement and Control Systems” (also referredto as, “Precision Time Protocol”) was developed to enable synchronizingclocks between devices connected by a network. Using the IEEE 1588protocol, to achieve the highest precision, for example in thenanosecond range, dedicated hardware is used that detectssynchronization packets on the network and adjusts a clock accordingly.In conventional approaches to clock synchronization, a software-onlyimplementation of IEEE 1588 is available in an open source applicationcalled “PTPd” (Preciscion Time Protocol daemon). PTPd is able tosynchronize the software system clocks on multiple systems withmicrosecond precision. PTPd does not control a hardware clock, butadjusts the time-of-day value in the operating system. As such, the IEEE1588 protocol and the PTPd technique can be used to synchronize thesoftware clocks 120A-120C included in the measurement devices to themaster clock 115 via a packet-switched network, such as Ethernet.

Embodiments of the disclosure build on top of such a software-onlyimplementation of IEEE 1588 (such as PTPd). First, the master clock 115is synchronized to the PPS pulse from the GPS module 112 by thecontroller 114. Then, the software clocks 120A-120C included in themeasurement devices are synchronized to the master clock 115 using asoftware-only implementation of IEEE 1588 (such as PTPd). Once thesoftware clocks 120A-120C included in the measurement devices aresynchronized to one another, the corresponding controllers 122A-122C,respectively, are configured to synchronize the hardware clocks124A-124C to the corresponding software clocks 120A-120C, respectively.As such, the hardware clocks 124A-124C become synchronized to oneanother. The measurement data collected by the measurement devices isnow synchronized in time.

The measurement data can be transmitted to the computing subsystem 110for computation of gas flux values, as described above. The results canbe transmitted back to the measurement devices for storage or to the webmonitor device 116, as also described above, where the results may bedisplayed.

As such, embodiments of the disclosure provide for systems and methodsfor computing gas flux values in real-time or near-real-time usinginstruments connected over Ethernet. In further embodiments, the clocksynchronization method disclosed herein could also be used in any devicegenerating a data stream to allow that data to be merged with data fromanother device.

FIG. 2 illustrates a gas flux measurement system, according to oneembodiment. Many of the components shown in FIG. 2 are described in FIG.1 and are not repeated for clarity. One difference between FIG. 1 andFIG. 2 is that in FIG. 2, the wind speed measuring device 104 is notconnected to the gas analyzer 106 via the data communication path 126(nor is the wind speed measuring device 104 connected directly to thecomputing subsystem 110 via the data communication path 126). Rather,the wind speed measuring device 104 is connected to the gas analyzer 106via an analog connection 202. As such, an analog-to-digital (A/D)converter 204 included in the gas analyzer 106 is configured to samplethe raw analog wind data received from the wind speed measuring device104. The raw data can be sampled based on the hardware clock 124Cincluded in the gas analyzer 106. As described above, the hardware clock124C is synchronized to the other hardware clocks 124A-124B included inthe system by way of the corresponding software clocks, and ultimatelyby way of the master clock 115 and pulses from the GPS module 112.

FIG. 3 is a block diagram of example functional components for acomputing subsystem 110, according to one embodiment. One particularexample of computing subsystem 110 is illustrated. Many otherembodiments of the computing subsystem 110 may be used. In theillustrated embodiment of FIG. 3, the computing subsystem 110 includesone or more processor(s) 311, memory 312, a network interface 313, oneor more storage devices 314, a power source 315, and input device(s)380. The computing subsystem 110 also includes an operating system 318and a communications client 340 that are executable by the client. Eachof components 311, 312, 313, 314, 315, 360, 380, 318, and 340 isinterconnected physically, communicatively, and/or operatively forinter-component communications in any operative manner.

As illustrated, processor(s) 311 are configured to implementfunctionality and/or process instructions for execution within computingsubsystem 110. For example, processor(s) 311 execute instructions storedin memory 312 or instructions stored on storage devices 314. Memory 312,which may be a non-transient, computer-readable storage medium, isconfigured to store information within computing subsystem 110 duringoperation. In some embodiments, memory 312 includes a temporary memory,area for information not to be maintained when the computing subsystem110 is turned OFF. Examples of such temporary memory include volatilememories such as random access memories (RAM), dynamic random accessmemories (DRAM), and static random access memories (SRAM). Memory 312maintains program instructions for execution by the processor(s) 311,such as the computation software 113 shown in FIGS. 1-2 for computinggas flux from measurement data.

Storage devices 314 also include one or more non-transientcomputer-readable storage media. Storage devices 314 are generallyconfigured to store larger amounts of information than memory 312.Storage devices 314 may further be configured for long-term storage ofinformation. In some examples, storage devices 314 include non-volatilestorage elements. Non-limiting examples of non-volatile storage elementsinclude magnetic hard disks, optical discs, floppy discs, flashmemories, or forms of electrically programmable memories (EPROM) orelectrically erasable and programmable (EEPROM) memories.

The computing subsystem 110 uses network interface 313 to communicatewith external devices via one or more networks, such as the gasanalyzers 102, 106 and wind speed measuring device 104 shown in FIGS.1-2. Network interface 313 may be a network interface card, such as anEthernet card, an optical transceiver, a radio frequency transceiver, orany other type of device that can send and receive information. Othernon-limiting examples of network interfaces include wireless networkinterface, Bluetooth®, 3G and WiFi® radios in mobile computing devices,and USB (Universal Serial Bus). In some embodiments, the computingsubsystem 110 uses network interface 313 to wirelessly communicate withan external device, a mobile phone of another, or other networkedcomputing device, such as web monitor device 116.

The computing subsystem 110 includes one or more input devices 380.Input devices 380 are configured to receive input from one or moresources. Non-limiting examples of input devices 380 include a GPS module308, or any other type of device for detecting a command or sensing theenvironment.

The computing subsystem 110 includes one or more power sources 315 toprovide power to the computing subsystem 110. Non-limiting examples ofpower source 315 include single-use power sources, rechargeable powersources, and/or power sources developed from nickel-cadmium,lithium-ion, or other suitable material. In some embodiments, the powersource 315 is a solar power source. Also, in some embodiments, the powersource 315 can be internal to or external to the computing subsystem110. Also, in some embodiments, power source 315 provides power to thecomputing subsystem 110 as well as to the measurement devices (e.g.,devices 102, 104, 106).

The computing subsystem 110 may include an operating system 318. Theoperating system 318 controls operations of the components of thecomputing subsystem 110. For example, the operating system 318facilitates the interaction of communications client 340 with processors311, memory 312, network interface 313, storage device(s) 314, inputdevice 180, output device 160, and power source 315. For example, theoperating system 318 may control the master clock 115 of the computingsubsystem 110.

As also illustrated in FIG. 3, the computing subsystem 110 includescommunications client 340. Communications client 340 includescommunications module 345. Each of communications client 340 andcommunications module 345 includes program instructions and/or data thatare executable by the computing subsystem 110. For example, in oneembodiment, communications module 345 includes instructions causing thecommunications client 340 executing on the computing subsystem 110 toperform one or more of the operations and actions described in thepresent disclosure. In some embodiments, communications client 340and/or communications module 345 form a part of operating system 318executing on the computing subsystem 110.

FIG. 4 is a flow diagram of method steps for measuring gas flux,according to one embodiment. As shown, the method 400 begins at step402, where a computing device, such as computing subsystem 110, receivesa master clock signal from a global positioning system (GPS) module. Themaster clock signal may be a PPS pulse. The computing device uses themaster clock signal to set a master clock included in the computingdevice.

At step 404, the computing device transmits a clock synchronizationsignal to a measurement subsystem configured to measure environmentaldata, where the measurement subsystem comprises at least two clocks. Inone embodiment, the clock synchronization signal is transmitted over apacket-switched network, such as Ethernet. For example, the measurementsubsystem may comprise two or more measurement devices, such as gasanalyzers, wind analyzers, temperature analyzers, etc., configured tomeasure the environment. Each measurement device may include its ownhardware clock.

As described herein, in some embodiments, each measurement device isconfigured to receive the clock synchronization signal from thecomputing device and synchronize its own software clock to the masterclock. Then, by way of a controller included in the measurement device,each measurement device is configured to synchronize a hardware clockincluded in the measurement device to the corresponding software clock.The environment is sensed based on the timing information from thehardware clocks.

At step 406, the computing device receives the environmental data fromthe measurement subsystem, where the environmental data is associatedwith the at least two clocks. At step 408, the computing devicecalculates one or more gas flux values based on the environmental datareceived from the measurement subsystem. At step 410, the computingdevice transmits the calculated gas flux values to a remote computingdevice, via a data connection, where the gas flux value(s) may bedisplayed or further processed. Alternatively, the measured (andsynchronized) environmental data may be transmitted to a remote computersystem for further processing and calculation/computation.

FIG. 5 is a conceptual diagram of a computing subsystem 110, accordingto one embodiment. As shown, the computing subsystem 110 is coupled to aGPS receiver 112. The computing subsystem 110 may have a smallvolumetric footprint, so as to be easily mounted to a gas analyzer via amounting bracket 502, as also shown in FIG. 5. The example shown in FIG.5 is merely an example of a computing subsystem 110 and does not limitthe scope of embodiments of the disclosure.

In sum, embodiments of the disclosure provide systems and methods forsynchronization, management, and real-time or near-real-time calculationof gas flux. The systems and methods can be fully integrated withcommercially available analyzers and analyzer interface units. Thesystems and methods provide fully corrected, real-time fluxcomputations, remote access via a data connection (e.g., cellular orsatellite modem, for example), built-in GPS for synchronizing data,precision clock control, coordinate information, inter-site datacomparison, a low power draw, rugged construction, and rapidcommunication via Ethernet. According to various embodiments, integrateddata transfer and file viewing software within the computing subsystem110 and/or web monitor device 116 allows for automated data transfer atuser-specified intervals, site monitoring, diagnostics, and charting.Conventional systems that only “estimate” flux rates can introduce largeerrors when compared to the disclosed systems and methods, which usefinal, fully corrected flux rates processed by computation software.

Advantageously, the disclosed system synchronizes the clocks of variousmeasurement devices over an asynchronous, packet-switched network (suchas Ethernet), which provides for ease of installation and maintenancewhen providing a gas flux measurement system and method. For example,one advantage to using Ethernet is that a system implementingembodiments of the disclosure can connect many Ethernet devices togetherfrom different manufactures and scale up the system easily.

While the present disclosure has been described by way of example and interms of the specific embodiments, it is to be understood that thepresent disclosure is not limited to the disclosed embodiments. To thecontrary, it is intended to cover various modifications and similararrangements as would be apparent to those skilled in the art.Therefore, the scope of the appended claims should be accorded thebroadest interpretation so as to encompass all such modifications andsimilar arrangements.

All references, including publications, patent applications and patents,cited herein are hereby incorporated by reference to the same extent asif each reference were individually and specifically indicated to beincorporated by reference and were set forth in its entirety herein.

The use of the terms “a” and “an” and “the” and similar referents in thecontext of describing the disclosure (especially in the context of thefollowing claims) are to be construed to cover both the singular and theplural, unless otherwise indicated herein or clearly contradicted bycontext. The terms “comprising,” “having,” “including,” and “containing”are to be construed as open-ended terms (i.e., meaning “including, butnot limited to,”) unless otherwise noted. Recitation of ranges of valuesherein are merely intended to serve as a shorthand method of referringindividually to each separate value falling within the range, unlessotherwise indicated herein, and each separate value is incorporated intothe specification as if it were individually recited herein. All methodsdescribed herein can be performed in any suitable order unless otherwiseindicated herein or otherwise clearly contradicted by context. The useof any and all examples, or exemplary language (e.g., “such as”)provided herein, is intended merely to better illuminate the disclosureand does not pose a limitation on the scope of the disclosure unlessotherwise claimed. No language in the specification should be construedas indicating any non-claimed element as essential to the practice ofthe disclosure.

One embodiment of the disclosure may be implemented as a program productfor use with a computer system. The program(s) of the program productdefine functions of the embodiments (including the methods describedherein) and can be contained on a variety of computer-readable storagemedia. Illustrative computer-readable storage media include, but are notlimited to: (i) non-writable storage media (e.g., read-only memorydevices within a computer such as CD-ROM disks readable by a CD-ROMdrive, flash memory, ROM chips or any type of solid-state non-volatilesemiconductor memory) on which information is permanently stored; and(ii) writable storage media (e.g., floppy disks within a diskette driveor hard-disk drive or any type of solid-state random-accesssemiconductor memory) on which alterable information is stored.

Preferred embodiments of this disclosure are described herein, includingthe best mode known to the inventors for carrying out the disclosure.Variations of those preferred embodiments may become apparent to thoseof ordinary skill in the art upon reading the foregoing description. Theinventors expect skilled artisans to employ such variations asappropriate, and the inventors intend for the disclosure to be practicedotherwise than as specifically described herein. Accordingly, thisdisclosure includes all modifications and equivalents of the subjectmatter recited in the claims appended hereto as permitted by applicablelaw. Moreover, any combination of the above-described elements in allpossible variations thereof is encompassed by the disclosure unlessotherwise indicated herein or otherwise clearly contradicted by context.

We claim:
 1. A system for measuring gas flux, the system comprising: ameasurement subsystem configured to measure environmental dataassociated with measuring the gas flux, wherein the environmental datacomprises at least wind speed data and gas concentration data, whereinthe measurement subsystem comprises at least a first measurement devicehaving a software clock and a first hardware clock and a secondmeasurement device having a second hardware clock; and a computingsubsystem in signal communication with the measurement subsystem,wherein the computing subsystem is configured to: transmit a clocksynchronization signal over a packet-switched network to the measurementsubsystem so as to synchronize the first hardware clock in the firstmeasurement device in the measurement subsystem, wherein the clocksynchronization signal is based on a master clock signal, wherein thesoftware clock is synchronized based on the clock synchronizationsignal, and wherein the first hardware clock is synchronized by thesoftware clock to the master clock signal, receive the environmentaldata from the measurement subsystem, wherein the environmental data isassociated with the first and second hardware clocks, re-sample theenvironmental data received from the second measurement device based onthe master clock signal so that the environmental data from the firstand second measurement devices are synchronized in time to the masterclock signal, and calculate the gas flux based on the synchronizedenvironmental data.
 2. The system of claim 1, wherein the system isinstalled above a terrestrial surface or a water surface.
 3. The systemof claim 1, wherein the environmental data comprises gas concentrationdata and vertical wind speed data.
 4. The system of claim 1, wherein themeasurement subsystem comprises a gas analyzer configured to analyzecarbon dioxide and water vapor.
 5. The system of claim 4, wherein themeasurement subsystem further comprises an anemometer.
 6. The system ofclaim 1, wherein the measurement subsystem comprises a first gasanalyzer, a second gas analyzer, and an anemometer, wherein the firstgas analyzer is configured to analyze methane and the second gasanalyzer is configured to measure carbon dioxide and water vapor.
 7. Thesystem of claim 1, further comprising: a global positioning system (GPS)module communicatively coupled to the computing subsystem, wherein theGPS module is configured to transmit a signal to the processing unitthat corresponds to the master clock signal.
 8. The system of claim 7,wherein the signal comprises a PPS (pulse-per-second) signal.
 9. Thesystem of claim 1, wherein the first and second hardware clocks compriseFPGA (field-programmable gate array) clocks.
 10. The system of claim 1,wherein the computing subsystem is further configured to receive themaster clock signal from a global positioning system (GPS) modulecommunicatively coupled to the computing subsystem.
 11. The system ofclaim 1, wherein the packet-switched network comprises an Ethernetnetwork.
 12. The system of claim 1, wherein the computing subsystem isfurther configured to: transmit the calculated gas flux to a computingdevice communicatively coupled to the computing subsystem over a datanetwork.
 13. The system of claim 12, wherein the data network is awireless network or a wired network.
 14. The system of claim 12, whereinthe packet-switched network is the same as the data network, or whereinthe packet-switched network is different than the data network.
 15. Thesystem of claim 1, wherein environmental data measured by the secondmeasurement device is transmitted to a third measurement device; andwherein the third measurement device transmits the environmental datameasured by the second measurement device to the processing unit.
 16. Acomputing device for calculating gas flux, the computing devicecomprising: a controller including one or more processors, thecontroller configured to receive a master clock signal from a globalpositioning system (GPS) module; a network interface configured totransmit a clock synchronization signal that is based on the masterclock signal to a measurement subsystem configured to measureenvironmental data, wherein the environmental data comprises at leastwind speed data and gas concentration data, wherein the measurementsubsystem comprises at least a first measurement device having asoftware clock and a first hardware clock and a second measurementdevice having a second hardware clock; the network interface configuredto receive the environmental data from the measurement subsystem,wherein the environmental data is associated with the first and secondhardware clocks, wherein the environmental data received from the firstmeasurement device is synchronized to the master clock signal; and thecontroller being further configured to re-sample the environmental datareceived from the second measurement device based on the master clocksignal so that the environmental data from the first and secondmeasurement devices are synchronized in time to the master clock signal;and to calculate gas flux based on the synchronized environmental data.17. The computing device of claim 16, wherein the measurement subsystemcomprises a gas analyzer and an anemometer, wherein the gas analyzer isconfigured to analyze carbon dioxide and water vapor.
 18. A method forcalculating gas flux, comprising: receiving a master clock signal from aglobal positioning system (GPS) module; transmitting a clocksynchronization signal that is based on the master clock signal to ameasurement subsystem configured to measure environmental data, whereinthe environmental data comprises at least wind speed data and gasconcentration data, wherein the measurement subsystem comprises at leasta first measurement device having a software clock and a first hardwareclock and a second measurement device having a second hardware clock;synchronizing the software clock based on the clock synchronizationsignal, and synchronizing the first hardware clock by the software clockso that the first hardware clock is synchronized in time to the masterclock signal; receiving the environmental data from the measurementsubsystem, wherein the environmental data is associated with the firstand second hardware clocks; re-sampling the environmental data receivedfrom the second measurement device based on the master clock signal sothat the environmental data from the first and second measurementdevices are synchronized in time to the master clock signal, andcalculating gas flux based on the synchronized environmental data. 19.The method of claim 18, further comprising transmitting the calculatedgas flux to a computing device over a data network.
 20. The method ofclaim 18, wherein the measurement subsystem comprises a gas analyzer andan anemometer, wherein the gas analyzer is configured to analyze carbondioxide and water vapor.